Electronics consultant John Dunn has published a piece on accidental slot antennas in printed circuit boards on the EDN Network, showcasing how the same mitigation techniques used in the microwave industry can apply to high-frequency circuit designs.

“Way back when, I described how a blundering engineering manager managed to sabotage a project by ordering that a microwave assembly housing be constructed with only four screws to hold an aluminium case together with one screw in each corner instead of with a multiplicity of screws along each edge,’ John explains. “The resulting slot antennas that were created along each seam between the box and its cover plate radiated like gang busters and the innards of that box could not function.”

John then goes on to highlight a multi-layer circuit board design operating at a near-1GHz frequency which had the same problem: unintentional radiated electromagnetic interference, the result of the various layers forming ‘slot antennas.’ The solution, despite the radically different technologies involved, is the same: “a multitude of vias connecting the upper and lower ground planes to reduce slot antenna effects,” effectively taking on the same role as the screws in the classic microwave assembly.

While ‘drill a load of holes in it’ may seem like a brute-force solution, John’s example shows that it most definitely works – and could prove a handy tool for anyone working on high-frequency designs.